Reproducing system



Jan. 10, 1939- w. J. ALBERSHEIM REPRODUC ING SYS TEM FIGS l/VI/E/V TOR W. J. AL BERSHE/M FIG. 7

rm/war W J. ALBERSHEIM REPRODUCING S YS TEM Filed June 4, 1936 2 Sheets-Sheet n m w w ALBERSHE/M WJ. Br

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ATTORNEY Jan. 10, 1939.

Patents 1,833,373 and 1,879,423.

Patented Jan. 10, 1939 UNITED STATES REPRODUCING SYSTEM Walter J. Albersheim, N

ew York, N. Y., assignor to Electrical Research Products, Inc., New York, N. Y-., a. corporation of Delaware Application June 4,

6 Claims.

This invention relates to a method and means of reproducing a sound record impressed upon a photographic film and particularly to a method and means of reproduction in which the light energy from the scanning beam is not uniform across the transverse width of the sound track.

Sound recording systems are known in which the sound is recorded as a series of laminae of constant length which are displaced laterally 0'5 1 the sound track in accordance with the sound.

The sound record may have a form of a transparent area in the middle of the sound track surrounded by two opaque areas on the marginal edges as shown in U. S. Patent 1,833,373, or the sound record may have the form of an opaque area in the center of the sound track surrounded by two transparent areas on the edges thereof as shown in U. S. Patent 1,879,423. Such sound records are reproduced by means of a balanced light sensitive circuit such as disclosed in U. S.

In the reproduction of such film records, the scanning beam has heretofore been of uniform intensity across the full width of the sound track and the beam of light from the scanning lamp has been so limited by the slit in the scanning plate that the beam impressed upon the film is of uniform height across the full Width of the sound track.

In the reproduction of a film sound record of this character it has been found that the larger part of the undesired noise, known as ground noise, is reproduced from the transparent areas of the record. In accordance with the present invention, the scanning beam is so shaped that the light energy impressed upon the transparent areas 5 of the film is less than the light energy impressed upon the non-transparent areas of the film. This result may be achieved in various ways, for example, the intensity of the light emitted by 40 the scanning lamp may be non-uniform across the width of the sound track or a plate having varying degrees of transmission for light may be interposed in the scanning beam or stops may be placed in the beam to vary the intensity of the 45 light on the track. If the beam of light is of uniform intensity across the full width of the sound track, the quantity of light energy impressed upon the film may be varied by means of an opaque mask having apertures therein which 50 are not of uniform height across the width of the sound track. In reproducing a record, such as shown in Fig. 2 of U. S. Patent 1,833,373, the scanning slit may take the form of two triangles of equal height, the apices of the triangles being located in the center of the sound track and the bases of the triangles being respectively located on the two marginal edges of the sound track. In the reproduction of a sound record, such as shown in Fig. 1 of U. S. Patent 1,879,423, the scan- 60 ning slit may have the form of two triangles, the

1936, Serial No. 83,514

bases of the triangles being located on the center line of the sound track and the apices of the triangles being located on the marginal outer edges of the sound track.

It is, however, not essential that the scanning beam should have the form of two triangles. If we consider the sound track as divided along the center of the track, the only requirement for undistorted reproduction is that the two halves of the scanning function lying on each side of the center line of the track must be reversely symmetrical to each other, and that each individual half of the scanning function must be inversely symmetrical with regard to the value at its center. Any construction of the scanning lamp with the optical system or the scanning slit which insures that the quantity of light energy impressed across the width of the sound track complies with the two requirements given above will result in an undistorted reproduction of the sound record.

In the drawings:

Fig. l diagrammatically represents a reproducing system embodying the invention;

Fig. 2 shows the type of record used in the system of Fig. 1;

Fig. 2A is a geometrical showing of the principle of the invention;

Figs. 3 to 7 show various forms of opaque plates having scanning slits embodying the invention;

Fig. 8 is a plan view of a reproducing system having two sets of stops in the optical system;

Fig. 9 is an elevation of the system in Fig. 8;

Fig. 10 is a plan view of a reproducing system having one set of stops; and

Figs. 11, 12 and 13 show alternative forms of the stops shown in Figs. 8, 9 and 10.

In Fig. 1, light from a suitable source I is focused by a lens system represented by the lens 2 on a film sound record 3 moved normal to the plane of the drawing at constant speed by known constant speed sprockets (not shown). The light transmitted through the film 3 is focused by a lens system represented by the lens 5, upon some optical splitting device, such as the prism 6. The two beams of light from the prism 6 respectively excite the two light sensitive devices 1 and B which may be selenium or photoelectric cells. The outputs of the two devices I and B are connected in opposed or push-pull relationship to the primary winding of the transformer 9. A suitable source it! supplies polarizing voltage to the devices I and 8. The output of the transformer 9, suitably amplified, is reproduced by a reproducing device 4. The signal may obviously be reproduced as an acoustic wave, may be rerecorded or otherwise utilized.

An opaque screen I l pierced by a scanning slit, may be interposed in the beam of light between the film 3 and the prism B. The screen H may also be located at other points in the scanning beam, as indicated by the dotted line I2. The invention may also be applied to reproducing systems in which the sound record is scanned by a beam of light reflected from the record.

Fig. 2 shows a known type of positive or reproduction film sound record suitable for use with the invention, having a dark or opaque area occupying substantially one-half of the width of the sound track, the remainder of the width of the sound track being substantially transparent. The dark area is, at all times, of constant width, but is laterally displaced across the record track in accordance with the recorded signal, thus producing two complete complementary records. In

the record shown in Fig. 2, these two records are exactly 180 degrees out of phase with each other but other values of phase difierence may be attained during recording.

When a record as shown in Fig. 2 is reproduced by a scanning beam of rectangular cross-section formed by the known rectangular aperture, the beam impressed on the record is of constant height lengthwise of the film, thus the light energy is impressed equally on the opaque and transparent areas of the film. The transparent areas of the film tend. to produce undesired sounds, known as ground noise. In accordance with the present invention, the light energy is not uniform laterally of the record but is modified so that the light energy impressed on the opaque area of the film is greater than the light energy impressed on the transparent areas of the film. This variation in the light energy may be caused by the insertion in the beam of an optical member of varying light transmitting power, or it may be a Variation in the height of the scanning beam laterally of the record caused by the insertion in the beam of an opaque plate having a scanning aperture of unequal height, or it may be a variation in intensity of the light beam impressed on the light sensitive cells.

A variation in the intensity of the light in the scanning beam may be attained by suitable design of the filament of the scanning lamp, or by the insertion of an optical wedge of graduated transmitting power located either in front of the film at the dotted line l2, or between the film and the light sensitive cells, in connection with the scanning slit H. A double optical wedge must be used and, with the film shown in Fig. 2, the intensity of the light transmitted by the wedge must be greatest in the center of the film and least at either edge.

Fig. 3 shows an opaque mask pierced by a scanning aperture formed in accordance with the invention. The heights of the apertures at the center of the record will be equal and may be double the height of a rectangular aperture. The heights of the aperture diminish regularly from the center out to the edge of the record.

Fig. 4 shows an aperture plate similar to Fig. 3 but having the apertures longitudinally displaced for the reproduction of a film in which the two records are not exactly 180 degrees out of phase, while Fig. 5 shows an aperture plate for the reproduction of a film in which the two records are exactly 180 degrees out of phase with each other.

In order to avoid distortion, it is not essential that a tringular aperture be used in the aperture plate, or that the light energy impressed on the light sensitive cells should vary uniformly outward from the center line of the record. It is essential that the light energies at two points equidistant from the center line of the records shall be equal, thus producing a condition which may be termed reverse symmetry. Considering only one-half of the record, it is essential that the light energies at any two points equidistant from the center line of the half record (the quarter lines of the whole record) shall together equal a constant, thus producing a condition which may be termed inverse symmetry.

In Fig. 2A, the aperture plate of Fig. 5 is shown placed over a portion of the record shown in Fig. 2. The lines a and c show the full width of the aperture in the aperture plate and the full width of the sound record, 0 is the center line of the record and the aperture 1) is equidistant from a and 0 while d is equidistant from c and e. Thus, in order to have what is herein termed reverse symmetry the light energy impressed on the light sensitive devices, represented by any ordinate m located x units to the left of the center line 0, must equal the light energy impressed on the devices, represented by the ordinate 72 located +a: units to the right of the center line. And, in order to have what is herein termed inverse symmetry the light energy impressed on the light sensitive devices, represented by any ordinate 11 located -a units to the left of the quarterline (2, added to the light energy represented by the ordinate 0 located +2 units to the right of the quarter-line d must equal the light energy represented by the ordinate h on the center line 0. Thus, Fig. 7, if the height of the aperture is taken as two arbitrary units, the light energies transmitted at any two points equidistant from the center line of the record are equal, and the light energies transmitted at any two points in the half record equidistant from the center line of the half record will together equal two. Providing the height of the aperture varies in accordance with these two limitations, irregularly shaped apertures, as illustrated in Fig. 6, may be used without producing distortion.

In Fig. 2A, the rectangle k l f g indicates the conventional rectangular aperture, the triangle f h g an aperture made in accordance with the present invention. In the conventional aperture, the rectangle 7' l g (1 represents light energy from the clear or imexposecl portion of the film. In the present invention, this energy is reduced to the triangle 7' g d, thus the ground noise is reduced to approximately one-half. It will be noted that the light energy from the left-hand record is reduced by the small triangle to the left of the point z, and this would normally result in distorting the reproduced sound. At the same time, however, the light energy from the right-hand record is increased by the small triangle to the left of the point 7'. As these small quantities of light are approximately equal, and the light sensitive devices are connected so that the currents due to reproduction of the records are added, no distortion of the sound will be produced.

In Figs. 8 and 9, light from the filament H. of a scanning lamp is focussed by the lens system E3 on a film sound record M. An image of the illuminated width of the sound record M is formed by the lenses l5, it in the plane of the rear scanning slit H. The rear scanning slit H and the remainder of the system may be the beam are located at the intersection of the lines drawn from the center of the image to the edges of the lens stop and the ends of the image to the opposite edges of the lens stop. Under these conditions, the intensity of the light at the center of the slit II will be a maximum and will decrease uniformly to zero at both ends of the slit l I. Imagine the eye to be placed at the upper end of the slit II. The uper edge of the stop ill will then be in line with the lower edge of the stop I! and no light will reach the eye, thus the intensity will be zero. Now, if the eye be moved a short distance nearer to the center of the slit il, a small part of the illuminated portion of the lens I6 will be seen and the intensity at this point will have some small value. As the eye is moved progressively nearer the center of the slit II, the intensity of the light will progressively increase until at the center of the slit II, the whole area of the aperture in the stop I1 contributes light and the intensity of the light is a maximum.

If the stop I8 is moved from the position shown nearer to the image plane in the slit H, the upper edge of the stop l8 will prevent any light from reaching a portion of the upper part of the slit H. Thus, in this case, the intensity of the light is a maximum for a short distance at the center of the slit ll, decreases uniformly to zero at a point in the upper part of the slit H and is zero from that point to the end of the slit II.

If the stop I8 is moved nearer the lens IS, the intensity of the light will be a maximum at the center of the slit II (but will be less in absolute magnitude) and will decrease uniformly to the ends of the slit II but will not be zero at the ends.

In Figs. 8, 9 and 10, similarly numbered elements have similar functions. In Fig. 10, the single unstopped lens l5 replaces the stopped lens system l5, l6, ll of Figs. 8 and 9. In this case the lines are drawn from the center and ends of the image to the edges of the lens IS.

The interposition of the stops l8 will cause the intensity of illumination of the image formed in the plane of the slit plate I I to vary from a maximum at the center to a minimum at each end.

The stops [8 may be formed of'two parallel plates or of a rectangular aperture in a single plate, as shown in Fig. 13. The aperture may also be formed as shown in Figs. 11 and 12, in which the radii of all the curves are one-half of the distance between the intersections of the lines shown on Figs. 8 and 10.

While certain specific embodiments of the invention have been disclosed, it will be evident that many variations may be made within the scope of the invention. For example, the stop i8 may be located between the lens i3 and the film i4 and cause the intensity of the light impressed on the film to vary as described hereinabove.

What is claimed is:

1. The method of reproducing a film sound record which comprises exposing a film sound record to light energy, the light energy impressed upon one-half of the track varying in reverse symmetry with the light energy impressed upon the other half of the track and the light energy impressed on either half of the track varying in inverse symmetry with regard to the value of the light energy at the center of that half of the track, individually transforming the light energy transmitted through each half of the sound track into a separate electrical current, combining said electrical currents in phase with each other and reproducing the combined electrical current.

2. The method of reproducing a film sound record which comprises exposing said record to a beam of light, the quantity of light impressed upon said record decreasing uniformly from the center of he record outward to both margins of the record, individually converting the light energy transmitted through both halves of said record into two electric currents, combining the two electric currents in proper phase into one current and reproducing said combined currents.

3. In a sound reproducing system, in combination, a photographic sound record having two complete complementary sound wave representations, means for impressing upon each of said representations a quantity of light energy varying in reverse symmetry with regard to the value of the light energy impressed on the other record, said quantities of light energy being in inverse symmetry with regard to the value at the center of each, a pair of light sensitive devices individually excited by the light transmitted through each of said records, means for combining the outputs of said two light sensitive devices, and means for reproducing the combined outputs.

4. The method of reproducing a film sound record which comprises exposing said record to a beam of light, exciting a pair of light sensitive devices with the light from respective halves of the record, the quantity of light energy impressed on said devices normally decreasing from the center of said record outward to both margins of said record, individually converting the variations in light energy caused by the halves of said record into two electric currents, combining said currents in proper phase into one current, and reproducing said combined currents.

5. The method of reproducing a film sound record which comprises exposing said record to a beam of light, exciting a pair of light sensitive devices with the light from respective halves of the record, the light energy from one-half of the record varying in reverse symmetry with the light energy from the other half, and the light energy from either half varying in inverse symmetry with regard to'the light energy at the center of that half, individually converting the variations in light energy caused by the halves of said record into two electric currents, combining said currents in proper phase into one current and reproducing said combined currents.

6. In a sound reproducing system, a source of light, a photographic film having two complete complementary sound records, means for uniformly illuminating both said records from said source, a lens system for forming an image of said records, a pair of light sensitive devices respectively excited by the light from said records to produce two electric currents, means for combining said currents and reproducing the combined current, and an optical stop located between said lens system and the plane of said image to cause the light energy impressed on said devices to decrease symmetrically from the adjacent edges of said records to the outer edges.

WALTER J. ALBERSHEIM. 

